1. Technical Field
The present invention relates to an organic electroluminescence device.
2. Related Art
In recent years, a demand for flat display devices which consume less electric power and have a lighter weight has increased with an advance in diverse information apparatuses. As one of the flat display devices, an organic electroluminescence device (organic EL device) which performs a display by allowing an organic electroluminescence element (organic EL element) which has a function layer including an organic light emission layer to emit light was suggested.
The organic EL device is classified into two display types, that is, a so-called top emission type in which light emitted by the organic EL element is radiated in a side opposite a substrate for forming the organic EL element and a so-called bottom emission type in which the light emitted by the organic EL element is radiated in a substrate for forming the organic EL element by transmitting the substrate. When these two display types are compared to each other, a top emission type organic EL device is more advantageous in high resolution and high definition of a display picture, since it is easier to improve a pixel aperture ratio.
In the organic EL device, an electrode for radiating the light emitted from the light emission layer needs to have a light transmissive property. Accordingly, in the top emission type, a cathode (electrode) radiating light needs to have the light transmissive property. The light transmissive property is granted to the light transmissive cathode (electrode), by using a transparent conductive material such as ITO (Indium Tin Oxide) or sufficiently forming a metal material (alloy material) such as MgAg in a thin film.
However, in the transparent (light transmissive property) cathode, a resistance value is increased due to a property (conductivity) of a formation material or a small cross-section area of the cathode formed in a thin film. Therefore, in a case of a large-scale organic EL display (organic EL device), since irregularity of brightness between the organic EL elements is caused in the outer circumference and the inside of a display area, for example, due to a voltage drop of the cathode resulting from the increased resistance value, a problem may occur in that a display quality deteriorates due to display unevenness such as light emission unevenness or bright unevenness.
In order to solve this problem, there was suggested a method of realizing a substantially low resistance value of the transparent cathode and solving the problem with the display unevenness by forming an auxiliary wire in state where the auxiliary wire is conductive to the transparent cathode and setting a resistance value of a transparent electrode to a total resistance value obtained by adding the resistance values of the transparent cathode and the auxiliary wire (see JP-A-2005-158583).
However, in the organic EL element, when a polymer material is used for a function layer forming material, a wet coating method (liquid phase method) is used for applying and arranging a liquid substance (function liquid) containing the function layer forming material at a predetermined location and evaporating a solvent to form a desired film (function film) of a formation material.
As one effective method of the various wet coating methods, a manufacture method using a liquid-droplet ejecting method is known. An ink jet method of the liquid-droplet ejecting method has various advantages in that a mask is not necessary in patterning, separate coating of high resolution is possible, less ink is lost, coating of a large area is easy, and the like. Accordingly, the ink jet method is suitable for performing the separate coating to form the function film in a minute pattern, for example, a minute RGB pattern for a full color display, thereby realizing an organic EL device which has a high resolution and a high quality.
In the manufacture method using the liquid-droplet ejecting method, partition walls are provided in the vicinity of an area where the function liquid is coated to partition arrangement locations of the function liquid. When the partition walls are provided, a location precision can be improved and the function liquid coated at one area can be also prevented from being mixed with the function liquid coated in another area.
The partition walls are used not only for the wet coating method but also for a gas phase method such as a vapor deposition method. By using the partition walls, an insulation property can be ensured by preventing short circuit between pixel electrodes (anodes), pixels can be separated from each other even when the function layer is formed on an entire surface by the vapor deposition method, and a problem of not obtaining a desired display performance can be prevented.
The partition walls are formed so as to have a height in the range of about 1 to 3 μm, for example, in accordance with a method of forming the function layer. On the other hand, when the transparent cathode is formed as a thin film in order to guarantee a light transmissive property, the transparent cathode has a thickness in the range of about 5 to 10 nm by the vapor deposition method or the like. For example, the transparent cathode is formed as a thin film so as to have a thickness of about 10 nm, when MgAg is used.
In this case, since the transparent cathode is considerably thinner than the height of the partition walls, step disconnection may occur due to a step difference formed in a side surface of the partition wall. Therefore, line disconnection may occur in a portion covering the function layer formed in a concave portion in the partition wall from the cathode on the partition wall. That is, when the portion covering the function layer of the concave portion in the partition wall is not electrically connected to the cathode, current does not flow in the function layer and thus light is not emitted.